Ann L. Rypstra

Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae)

Some prey can distinguish between chemical cues from predators fed different diets. Here we document the first evidence of diet-based chemical discrimination of predators in a terrestrial arthropod and measure the survival value of behavioural responses to predator chemical cues. We tested activity level and avoidance behaviour of the wolf spider, Pardosa milvina, to faeces and silk associated with the predatory wolf spider, Hogna helluo, fed either P. milvina or crickets (Acheta domesticus). We then measured survival of Pardosa in the presence of Hogna when placed on blank paper or paper previously occupied by Hogna fed either crickets or Pardosa. Filter paper previously occupied by Hogna from each diet treatment or a blank control were simultaneously presented to adult female Pardosa among four treatment pairs (N=15/treatment): (1) blank paper/blank paper, (2) Hogna fed crickets/blank, (3) Hogna fed Pardosa /blank and (4) Hogna fed Pardosa / Hogna fed crickets. Cues from Hogna fed either crickets or Pardosa elicited significantly less activity relative to blank controls. Cues from Hogna fed Pardosa elicited a significantly greater reduction in activity than Hogna fed crickets. When given a choice, Pardosa initially chose the blank substrate significantly more often than either substrate with Hogna cues. Spiders survived longer in the presence of cues from either Hogna diet treatment relative to blank paper, but there was no significant effect of predator diet on survival. Results suggest diet-based predator cues elicit different levels of activity in Pardosa that reduce predation in the presence of Hogna. Copyright 2001 The Association for the Study of Animal Behaviour.

Habitat selection in a large orb-weaving spider: vegetational complexity determines site selection and distribution

1. The distribution of the large orb‐weaving spider Argiope trifasciata in old field habitats of North America and the habitat selection process this species used was studied for 2 years.

Top-Down Effects in Soybean Agroecosystems: Spider Density Affects Herbivore Damage

Spiders are abundant predators in many agricultural systems. The goal of this study was to determine if the influence of spiders as predators could cascade through the food web and affect primary producers. We examined the effects of spider augmentation and removal in soybean monocultures to assess their impact on the damage experienced by the plants. In two of three years (1990 and 1992), leaf damage was reduced in areas where spiders were added, and in one of two years (1992), there was increased damage in areas where spiders were removed. The biomass of insects killed by the spiders was positively correlated with spider mass and the leaf damage near augmentation sites was negatively correlated with the mass of insects killed by the spiders. In this study, small changes in spider density had a significant localized effect on the plants, especially in years when damage due to pest insects was high. These data also verified that trophic cascades and top-down control are in operation at measurable levels in soybean food webs

WOLF SPIDERS SHOW GRADED ANTIPREDATOR BEHAVIOR IN THE PRESENCE OF CHEMICAL CUES FROM DIFFERENT SIZED PREDATORS

The wolf spider, Pardosa milvina, displays effective antipredator behavior (reduced activity) in the presence of silk and excreta cues from adults of another cooccurring wolf spider, Hogna helluo. However, Pardosa and Hogna engage in size-structured intraguild predation, where Pardosa may be either the prey or predator of Hogna. We tested the ability of adult female Pardosa to vary antipredator responses toward kairomones produced by Hogna that vary in size. Hogna were maintained on filter paper for 24 hr. We then presented the paper to adult female Pardosa simultaneously paired with a blank sheet of paper. One treatment had two sheets of blank paper to serve as a control. The Hogna stimulus treatments were as follows (N = 15/treatment): (1) 1 Hogna half the mass of Pardosa; (2) 1 Hogna of equal mass of a Pardosa; (3) 1 adult Hogna, 30 times the mass of Pardosa; and (4) 8 Hogna each 0.25 the mass of Pardosa. Pardosa decreased activity in the presence of kairomones from Hogna of equal or larger size, but showed no change in activity in the presence of a blank control or from a single Hogna smaller than itself. Pardosa showed a reduction in activity in the presence of cues from eight small Hogna. Pardosa avoided substrates with adult Hogna cues, but showed no avoidance response to any other treatment. These results suggest that Pardosa is showing graded antipredator behavior relative to the quantity of predator kairomones present rather than directly discriminating among the different sizes of the predator.

The effects of hunger on locomotory behaviour in two species of wolf spider (Araneae, Lycosidae).

We compared the influence of recent feeding history on locomotory behaviour in two species of wolf spiders, Hogna helluo (Walckenaer) and Pardosa milvina Hentz, in the laboratory. Both species are cursorial hunters. We maintained the spiders in the laboratory on satiation and stringent feeding regimes and measured their locomotory activity levels for 1 h using a digital activity recording device. We subjected H. helluo to either ad libitum feeding for 14 days or no food for 14 days. We subjected P. milvina to ad libitum feeding or fasting treatments for 7 and 14 days. We found that H. helluo showed a shift in locomotory activity depending on feeding regime, whereas P. milvina did not. Food-limited H. helluo travelled further than satiated H. helluo, and did so by moving more frequently. Pardosa milvina was in general much more active than H. helluo. We propose that P. milvina is an active forager compared with the sit-and-wait strategy of H. helluo. This difference in foraging strategy is correlated with differences in body size and habitat use. Copyright 1999 The Association for the Study of Animal Behaviour.

PREY SIZE, SOCIAL COMPETITION, AND THE DEVELOPMENT OF REPRODUCTIVE DIVISION OF LABOR IN SOCIAL SPIDER GROUPS

It has been suggested that the cooperatively social spider, Anelosimus eximius, is eusocial. It has overlapping generations and cooperative brood care, and some females in colonies never reproduce. The hypothesis that the reproductive division of labor arises because of social competition over large prey was tested. Groups of sibling females were provided two types of prey that differed primarily in size. The absolute amount of each type of prey provided fell into three categories. The timing of molt to adulthood and subsequent production of egg sacs was monitored. More spiders molted to adulthood on small fruit flies than on larger houseflies, but the spiders that made it to adulthood in the groups fed larger prey grew larger and produced more egg sacs than the adults on fruit flies at all prey levels. These data suggest that the cooperative capture of large prey in natural colonies influences the formation of a dominant-subordinate dichotomy in which dominants are able to monopolize the resources and secure sufficient resources to reproduce. This system may be important to colony survival because it allows some reproduction to take place even at low prey availability. Likewise, it is possible to envisage such a systems being important to the evolution of the more complex reproductive division of labor with fixed reproductive and nonreproductive castes.

Airborne Chemical Communication in the Wolf Spider Pardosa milvina

Most studies involving chemical communication in spiders focus on contact pheromones attached to spider silk. Here we tested if males of the wolf spider Pardosa milvina use airborne pheromones to identify, locate, and follow females. Using a two-choice olfactometer, we tested the response of adult male P. milvina to a number of potential chemical cues while controlling for concomitant visual and vibratory stimuli. An airborne chemical cue from adult virgin female P. milvina elicited a positive taxis response from the male. We also tested adult male responses to penultimate instar female P. milvina, one adult male P. milvina, and two adult males together. In each case, test males showed no attraction to the stimuli. Additional experiments were run with pitfall traps baited with adult virgin female P. milvina as attractants. Again, we controlled for visual and vibratory cues from females. Pitfall traps containing virgin females captured significantly more males than control traps. Collectively, these experiments demonstrate evidence of an airborne sex pheromone in P. milvina.

A TEST FOR A DIFFERENTIAL COLONIZATION AND COMPETITIVE ABILITY IN TWO GENERALIST PREDATORS

Spatial subdivision of the landscape can reduce the intensity of interspecific interactions, whether they be predation or competition. Recent models examining the ways in which spatial pattern in the landscape will influence the outcome of species interactions assume a trade-off between colonization ability and competitive ability in the interacting species. We tested for differential colonization and competitive ability in two interacting species of wolf spider (Hogna helluo and Pardosa milvina) which co-occur in agricultural and early successional habitats in the eastern USA. We conducted our research in replicated experimental soybean plots in which we created islands of enhanced habitat by supplementing natural litter and enhancing weed growth. Our experimental manipulations were repeated once for each of the two spider species: (1) spiders added, (2) prey attractants (composted vegetable waste) added, (3) spiders and prey attractants added, and (4) one control, for a total of eight subplots. We replicated the experiment six times, three times each in conventionally tilled fields and conservation tilled fields. We censused these plots at the end of the summer and found that conspecific addition significantly elevated numbers of one species (H. helluo) but not the other (P. milvina). These findings were consistent with our predictions that H. helluo is limited in colonization ability when compared to P. milvina. The addition of prey attractants significantly elevated numbers of both species, but the effect was far stronger for the superior colonist (P. milvina). This indicates that P. milvina is able to track resource abundance (both habitat structure and prey), a trait correlated with colonization ability. We found no strong evidence for a negative effect of H. helluo addition on numbers of P. milvina, as would be predicted if H. helluo strongly competed with or significantly preyed upon P. milvina. Body condition of P. milvina was lowest in subplots with higher numbers of H. helluo, indicating that H. helluo may have influenced the foraging success of P. milvina. We also found a strong and unexpected effect of the context of the plots (background tillage regime) on numbers of P. milvina, with there being approximately twice the P. milvina in the subplots in conventionally tilled fields.

The effect of kleptoparasitism on prey consumption and web relocation in a Peruvian population of the spider Nephila clavipes

A high degree of mobility was observed in a population of Nephila clavipes (L.) (Araneae; Araneidae) in southeastern Peru, September-December, 1979. Prey capture and consumption were measured relative to the number of kleptoparasitic spiders (Araneae; Theridiidae; Argyrodes sp.) in the webbing. Those N. clavipes that moved their webs shortly after observation had consumed significantly fewer prey items than those that maintained their web site. However, total prey capture was not different between the two groups. Prey consumption was significantly reduced by each additional kleptoparasite in the web. Consequently, there was a complete correlation between the number of Argyrodes individuals in a spiders web and the percentage of those spiders that relocated their web.

Leg Autotomy in the Wolf Spider Pardosa milvina: A Common Phenomenon with Few Apparent Costs

Abstract A number of animals escape predation by sacrificing a body part. Spiders commonly lose legs in encounters with predators or conspecifics. We investigated the frequency of leg loss and its affect on locomotion and prey capture activities of the wolf spider, Pardosa milvina (Araneae; Lycosidae). In addition, we determined if Pardosa were easier to subdue by the larger wolf spider predator, Hogna helluo (Araneae; Lycosidae), once they had experienced leg loss. A field census demonstrated that Pardosa autotomized members of all pairs of legs with equal frequency but overall leg loss was high and increased significantly late in the season. Laboratory experiments revealed that leg loss had no effect on locomotory behavior or prey capture. However, injured spiders tended to take smaller prey. The ability of Hogna, to attack and subdue 7 or 8-legged Pardosa was not different, although 8-legged Pardosa tended to lose multiple legs as they were killed whereas 7-legged Pardosa only lost one. These data suggest that the costs of autotomizing one leg are marginal for Pardosa females and, thus, support the “spare leg hypothesis” that has been proposed for other arachnids.